1. Field of the Invention
This invention relates to a video camera which controls an image pickup action by serial communication.
2. Description of the Related Art
The control operation of every electronic apparatus has recently come to be carried out by using a microcomputer. In the case of a video camera, a control device of it includes a microcomputer. The control device is generally arranged to conduct serial communication with each applicable processing circuit for various purposes. For example, the constant of a signal processing circuit is changed. Data is taken into the control device from a white balance circuit, a light measuring circuit, an automatic focusing circuit, etc. An image pickup action is controlled according to such data.
FIG. 1 is a block diagram showing by way of example the arrangement of the conventional video camera. The video camera includes a focusing lens 1 which is arranged to be movable in the direction of an optical axis. An iris 2 is arranged in rear of the focusing lens 1 to adjust the quantity of incident light. An image sensor 3 is arranged in rear of the iris 2 to have an optical image of an object of shooting formed thereon and to photo-electrically convert the optical image into a video signal. The image sensor 3 is connected to a sample-and-hold (hereinafter referred to as CDS) circuit 4 which is arranged to sample and hold the video signal obtained from the image sensor 3. To the CDS circuit 4 is connected an analog-to-digital (A/D) converter 5 which is arranged to convert the output of the CDS circuit 4 into a digital video signal. The A/D converter 5 is connected to a signal processing circuit 6, a light measuring circuit 7 and an automatic focusing circuit 8 which are connected in parallel to each other. The signal processing circuit 6 is arranged to set a circuit gain and to convert the video signal into a TV signal by forming luminance and chrominance signals through various processes such as a gamma correction process, a blanking process, a synchronizing signal adding process, etc. The light measuring circuit 7 is arranged to detect the quantity of light obtained when an image is picked up. The automatic focusing circuit 8 is arranged to extract a focus signal, such as a high frequency component of the video signal.
The video camera has a microcomputer 12 arranged to perform overall control over an image pickup action. To the microcomputer 12 are connected a clock generator 25 which is arranged to output clock pulses, an iris driver 9 arranged to control the iris 2, and a motor driver 10. To the motor driver 10 is connected a motor 11 which is arranged to drive and move the focusing lens 1. Further, the microcomputer 12 is provided with a switch 21 which is arranged to perform switching between terminals R and S. To a common terminal of the switch 21 is connected a common terminal of another switch 28 which is arranged to perform switching between terminals A and D. A switch 24 has its common terminal connected to the terminal D of the switch 28 and is arranged to perform switching between terminals R1 and S1. The connecting relation between each of these switches and other parts of the video camera is as shown in FIG. 1. The switching actions of the switches 21, 28 and 24 are controlled by the microcomputer 12.
The signal processing circuit 6 includes a control shift register 13. The light measuring circuit 7 includes a control shift register 14 and a data shift register 15. The automatic focusing circuit 8 includes a control shift register 16 and a data shift register 17. The terminal R1 of the switch 24 is connected to the data terminal of the data shift register 17 and that of the data shift register 15. The terminal S1 of the switch 24 is connected to the data terminal of the control shift register 16, that of the control shift register 14 and that of the control shift register 13.
The terminal A of the switch 28 is connected to one of the data terminals of an address shift register 20. The output terminal of the clock generator 25 is connected to the control terminal of the address shift register 20. To the address shift register 20 are connected the input terminals of a decoder 19. The respective control terminals of the control shift register 13, the control shift register 14, the data shift register 15, the control shift register 16 and the data shift register 17 are connected to the output terminals of the decoder 19.
The conventional video camera which is arranged as described above operates as described below:
The microcomputer 12 transfers data to the signal processing circuit 6 in the following manner: In this case, the microcomputer 12 switches the connecting position of the switch 21 to the terminal S and that of the switch 28 to the terminal A. An address signal which indicates an address of the control shift register 13 is transferred from the microcomputer 12 to the address shift register 20 in accordance with the clock pulses applied from the clock generator 25. The decoder 19 reads the address of the control shift register 13 by decoding the address signal outputted from the address shift register 20 and supplies a setting signal to the control shift register 13 in such a way as to set the control shift register 13 into a shiftable state.
Under this condition, the microcomputer 12 switches connecting position of the switch 28 to its terminal D and that of the switch 24 to its terminal S1. Then, in accordance with the clock pulses from the clock generator 25, control data is transferred from the microcomputer 12 to the control shift register 13 which has been set into the shiftable state. Then, at the signal processing circuit 6, a TV signal is prepared by setting the circuit gain at an optimum value on the basis of the control data transferred from the microcomputer 12 to the control shift register 13. The TV signal thus obtained is outputted.
A data transferring action to be performed between the microcomputer 12 and the light measuring circuit 7 is next described as follows: The connecting position of the switch 21 is switched to the terminal S and that of the switch 28 is switched to the terminal A also in this instance. The microcomputer 12 then transfers an address signal which indicates an address of the control shift register 14 to the address shift register 20, according to the clock pulses coming from the clock generator 25. The decoder 19 decodes the address signal outputted from the address shift register 20 to read the address of the control shift register 14. The decoder 19 then supplies a setting signal to the control shift register 14 to set the control shift register 14 into a shiftable state.
Under this condition, the connecting position of the switch 28 is switched to the terminal D and that of the switch 24 is switched to the terminal S1. Then, light-measuring-position data is transferred from the microcomputer 12 to the control shift register 14 which has been set in the shiftable state, in accordance with the clock pulses coming from the clock generator 25. Upon receipt of the light-measuring-position data, the light measuring circuit 7 decides a light measuring position within an image plane on the basis of the light-measuring-position data transferred to the control shift register 14 from the microcomputer 12. A digital video signal corresponding to the light measuring position thus decided is integrated. The result of the integration process is stored in the data shift register 15 as light measurement data.
Next, the connecting position of the switch 28 is switched to the terminal A while the connecting position of the switch 21 remains at the terminal S. The microcomputer 12 then transfers an address signal indicating an address of the data shift register 15 to the address shift register 20 in accordance with the clock pulses coming from the clock generator 25. The decoder 19 reads the address of the data shift register 15 by decoding the address signal outputted from the address shift register 20 and supplies a setting signal to the data shift register 15 to set the data shift register 15 into a shiftable state. Under this condition, the connecting position of the switch 21 is switched to the terminal R, that of the switch 28 is switched to the terminal D and that of the switch 24 is switched to the terminal R1. The microcomputer 12 then inputs the light measurement data from the data shift register 15. The iris driver 9 is driven on the basis of the light measurement data thus obtained. As a result, the aperture of the iris 2 is controlled and adjusted to an optimum position according to the light measurement data.
The transfer of data between the microcomputer 12 and the automatic focusing circuit 8 is effected in the following manner: The connecting position of the switch 21 is switched to the terminal S also in this instance. The connecting position of the switch 28 is switched to the terminal A. The microcomputer 12 transfers an address signal which indicates an address of the control shift register 16 to the address shift register 20 according to the clock pulses coming from the clock generator 25. The decoder 19 reads the address of the control shift register 16 by decoding the address signal outputted from the address shift register 20. The decoder 19 then supplies a setting signal to the control shift register 16 to set the control shift register 16 into a shiftable state.
Under that condition, the connecting position of the switch 28 is switched to the terminal D and that of the switch 24 is switched to the terminal S1. The microcomputer 12 then transfers focus-detecting-position data to the control shift register 16 according to the clock pulses from the clock generator 25. The automatic focusing circuit 8 decides a focus detecting position within the image plane on the basis of the focus-detecting-position data transferred from the microcomputer 12. The automatic focusing circuit 8 then stores in the data shift register 17 a focus detection signal obtained at the focus detecting position as focus detection data.
Then, the connecting position of the switch 28 is switched to the terminal A while that of the switch 21 remains at the terminal S. The microcomputer 12 transfers an address signal indicating an address of the data shift register 17 to the address shift register 20 according to the clock pulses coming from the clock generator 25. The decoder 19 reads the address of the data shift register 17 by decoding the address signal outputted from the address shift register 20. The decoder 19 then supplies a setting signal to the data shift register 17 to set the data shift register 17 into a shiftable state. Under this condition, the connecting position of the switch 21 is switched to the terminal R, that of the switch 28 is switched to the terminal D and that of the switch 24 is switched to the terminal R1. The microcomputer then inputs the focus detection data from the data shift register 17. The motor driver 10 is driven on the basis of the focus detection data. The focusing lens 1 is moved along the optical axis so as to be adjusted to an optimum in-focus position.
However, in the case of the video camera described above, the data inputting and outputting directions to and from the data shift registers 15 and 17 and the control shift register 13, 14 and 16 are fixed. The direction of flow of data, i.e., whether the communication is to be started from the most significant bit (MSB) of data or from the least significant bit (LSB) is, therefore, fixedly decided in one direction depending on the arrangement of hardware. If the video camera is arranged to use an IC, therefore, the communication must be conducted in the fixed direction, so that if the video camera is arranged to use as a control device one of general purpose microcomputers which have different flows of serial data from each other, a usable microcomputer must be selected from a limited kinds of microcomputers.
Further, in the case of the conventional video camera described above, the speed at which data is inputted to and outputted from the data shift registers 15 and 17 and the control shift registers 13, 14 and 16 depends on the processing speed of the microcomputer 12. Therefore, if a microcomputer of a slow processing speed is employed as the control device, a long period of time is required for inputting and outputting data to and from the data shift registers 15 and 17 and the control shift registers 13, 14 and 16. The image pickup action of the video camera then would be affected by the slow processing speed.
This invention is contrived to solve the problems of the video camera described above. It is a first object of this invention to provide a video camera in which the direction of flow of data is arranged to be variable in such a manner that the flow of the data can be set either to begin with the MSB (most significant bit) of the data or to begin with the LSB (least significant bit) of the data.
It is a second object of this invention to provide a video camera which is arranged to permit use of a microcomputer of a low processing speed as a control device without lowing the performance of the video camera.
To attain the first object, a video camera arranged as a preferred embodiment of this invention includes processing means for processing a picked-up image signal outputted from image pickup means, control means for controlling an image pickup action of the image pickup means by transferring signals with the processing means, serial communication means disposed between the control means and the processing means for controlling the transfer of signals between the processing means and the control means, and change-over means for changing over an order of transmission of communication data within one unit to be transmitted by the serial communication means.
To attain the second object, a video camera arranged as another preferred embodiment of this invention includes processing means for processing a picked-up image signal outputted from image pickup means, control means for controlling an image pickup action of the image pickup means by transferring signals with the processing means, serial communication means disposed between the control means and the processing means for controlling the transfer of signals between the processing means and the control means, buffer means disposed midway in the serial communication means and arranged to store signal data, and speed change-over means for changing over the speed of data transmission by making the speed of data transmission to be effected on the side of the control means relative to the buffer means different from the speed of data transmission to be effected on the side opposite to the control means.
With the embodiment arranged in this manner, the control means controls the image pickup action of the video camera by transferring signals with the processing means which processes a picked-up image signal outputted from the image pickup means. In this instance, the serial communication means which is disposed between the control means and the processing means controls the transfer of signals between the processing means and the control means. The order of transmission of data within one unit to be transmitted by the serial communication means is changed from one order of transmission over to another order as necessary. By this change-over, the direction of flow of data transmission by the serial communication means is selectively decided as to whether the transmission is allowed to begin with the MSB of the data or to begin with the LSB of the data.
The control means is thus arranged to control the image pickup action of the video camera with signals transferred between the control means and the processing means. In this instance, the transfer of signals between the processing means and the control means is controlled by the serial communication means disposed between the control means and the processing means. Then, the speed of data transmission to be effected on the side opposite to the control means relative to the buffer means which is disposed midway in the serial communication means is set by the speed change-over means at a higher speed than the speed of data transmission to be effected on the side of the control means.
These and other objects an d features of this invention will become apparent from the following detailed description of embodiments thereof taken in conjunction with the accompanying drawings.